1. Field of the Invention
The present invention provides visible light curing systems, methods for reducing health risks to individuals exposed to systems designed to cure curable compositions by exposure to radiation, methods for bonding substrates and visible light curing compositions.
2. Brief Description of Related Technology
According to the U.S. Department of Labor's Occupational Safety and Health Administration (“OSHA”), non-ionizing radiation is a series of energy waves posed the oscillating electric and magnetic fields traveling at the speed of light. Non-ionizing radiation include suspected of ultraviolet, visible, infrared, microwave, radio frequency, and extremely low frequency area raises commonly operating the UV, visible and IR frequencies. UV radiation has a high photon energy range, and as such is particularly hazardous because there are usually no immediate symptoms of excessive exposure.
According to the U.S. Department of Health and Human Resources Center for Disease Control and Prevention's National Institute of Occupational Safety and Health (“NIOSH”) over exposure to UV radiation may result in the burning of exposed skin and have serious eye effects. Eye exposure is especially dangerous because the results of over exposure are not immediately evident. Long-term unprotected exposure can lead to partial loss of vision, accelerated skin aging an increased risk of skin cancer.
Unfortunately, no OSHA standard exists for UV radiation exposure. Nevertheless NIOSH has made recommendations for UV light in the spectral region of 200 to 400 nm, with limitations on exposure, particularly direct exposure to the eyes and skin, without protection, such as shaded glass barriers.
Apart from laser-generated radiation (in either the UV, IR or visible spectrum), no OSHA or NIOSH recommendations exist for exposure to visible radiation. And no OSHA standard exists for exposure to lasers, though their performance is regulated by the U.S. Department of Health and Human Resources Food and Drug Administration's Bureau of Radiological Health, under 21 CFR 1040.
Thus, the use of the UV radiation requires many precautions in order to limit worker and others exposure. Unlike radiation sources that generates UV radiation, apart from lasers, radiation sources that generates visible radiation are not accompanied by the same set of safety and health concerns.
It would be advantageous therefore to design, develop and offer a visible light curing system to allow workers and others to perform and observe the assembly of products using light curable compositions, without the attendant risk of their safety and/or health.
One potential source of visible light for use to cure photocurable compositions are light emitting diode (“LED”) devices, with a subset of such devices being organic light emitting diode devices.
A LED is a semiconductor device that emits incoherent narrow-spectrum light when electrically biased in the forward direction. This effect is a form of electroluminescence. The color of the emitted light depends on the chemical composition of the semiconducting material used, and can be near-ultraviolet, visible or infrared.
If the emissive layer material of an LED is an organic compound, it is known as an organic light emitting diode (“OLED”). To function as a semiconductor, the organic emissive material must have conjugated pi bonds. The emissive material can be a small organic molecule in a crystalline phase, or a polymer. Polymer materials can be flexible; such LEDs are known as PLEDs or FLEDs. Compared with regular LEDs, OLEDs are lighter and polymer LEDs can have the added benefit of being flexible.